Pulse width modulation (PWM) controllers are effectively being used to control voltage levels in power supplies and to control rotational speed and direction of motors. For motor control, a direct current (DC) power source is switched on and off at various rates to produce an alternating current (AC) waveform that is used to control the speed and rotational direction of the motor. Motors and some power loads require multiphase power, e.g., three phase power to operate. In a multiphase PWM power controller the PWM waveforms have the same frequency with a phase deference between each of the PWM waveforms, e.g., three-phase typically will be 120 degrees phase deference between PWM waveforms.
In a typical digital multiphase PWM generator circuit, there is a “master” time base circuit composed of a counter, a period register, and a digital comparator. The master counter counts up from zero until its value matches the value stored in the period register. When the comparator detects an equality situation between the master counter and the period register, the comparator generates a signal that resets the master counter and is broadcast to all of the individual PWM generator circuits. This master time base reset signal commands the individual PWM generator circuits to initialize their internal time base counters to predetermined values. Following the master time base counter reset signal, the individual time base counters count upward until they match the roll over value (period). Each of the individual counters can then reset and the counting process begins again (repeatedly).
Synchronizing multiphase PWM signals, that share the same period and duty cycle, with an external synchronization signal allows the multiphase PWM signals to acquire the same phase and period of the synchronizing signal. However, using an external synchronization signal to synchronize multiphase pulse width modulation (PWM) signals may be problematic with existing known PWM synchronization technologies. The sync signal provides both phase and period information, but existing external synchronization techniques only recover the phase information from the external sync signal. In multiphase PWM generation, the loss of sync period information yields corrupted multiphase PWM waveforms.